Coverage dependent structural changes during chlorine adsorption on Ag{110}

The adsorption of Cl₂ on Ag{110} at room temperature has been studied using angle-resolved static mode secondary ion mass spectrometry (SIMS), Auger spectroscopy, and LEED. The system has been examined over a coverage range from near zero to the p(2×1) overlayer structure observed by LEED. This structure could be produced by exposing the Ag{110} crystal to 2.5 L of Cl₂. The Cl LMM Auger spectra exhibited a distinct change in shape at about 1.0 L exposure which is attributed to a change in the electronic structure of the Ag-Cl bond. In addition, the SIMS Cl^- secondary ion yield deviated at this exposure from the expected exponential dependence on work function predicted by theory. An analysis of the secondary Cl^- ion kinetic energy distributions, and the polar and azimuthal angle distributions also suggests that the Cl atom is highly charged in the limit of zero coverage with an extended Ag-Cl bond length over that of bulk AgCl. As the coverage approaches the 1.0 L Cl₂ exposure point, however, there is significant weakening of surface dipoles due to adlayer interactions. This depolarization appears to be sufficient to allow significant contraction of the Ag-Cl bond length, such that the Cl atom may actually fall into the valley of the {110} surface. A submonolayer Cs overlayer appears to stabilize the negatively charged Cl adatoms, inhibiting the changes observed on the undoped Ag{110} surface. It is suggested that adlayer interactions which influence the formation of ordered overlayer structures mask important electronic and structural features of adsorbates which may only be observed in the single atom limit.